Electrocaloric effect in BaTiO₃ multilayer capacitors with first-order phase transitions

Abstract

Electrocaloric materials, presenting large adiabatic temperature change or isothermal entropy change under the application (or removal) of electric fields, offer an efficient alternative to caloric heat pumps for replacing hazardous gases used in traditional vapour-compression systems. Recently, a large electrocaloric temperature change of 5.5 K have been reported in Pb(Sc0.5Ta0.5)O3 multi-layered ceramic capacitors [1] thanks to its strong first-order phase transition and a temperature span of 13 K has been reported in a prototype based on these capacitors [2]. However, the toxicity of lead forces researchers to find eco-friendly materials exhibiting competitive electrocaloric performances. Here, we study the electrocaloric effect in lead-free BaTiO3 multilayer capacitors using an infrared camera. Unlike commercial BaTiO3 capacitors, we prepared our samples without sacrifying the first-order phase transition in BaTiO3. Their electrocaloric adiabatic temperature variations show two peaks versus temperature, which match BaTiO3 two first-order phase transitions, as observed by Differential Scanning Calorimetry. We measured a temperature drop of ~ 0.9 K over a temperature range of 70 K under 170 kV cm-1, starting at 30 °C near the tetragonal-to-orthorhombic phase transition. Under the same electric field, a maximum temperature change of 2.4 K was recorded at 126 °C, at BaTiO3’s Curie temperature. Our findings suggest that further optimized BaTiO3 capacitors could offer a path for designing lead-free caloric cooling prototypes.

Caloric effects in liquid crystal-based soft materials

“…Suitable materials are higher homologues of the n-alcyl cyanobiphenyl family of LCs (nCBs, n = 5-14) [23,24,26]. Homologues above the I-N-SmA triple point (n > 10) exhibit the direct first-order I-SmA phase transition with substantial latent heat that might provide an additional boost to the EC response [3,23,24,27]. Indeed, the direct EC measurements confirmed the existence of a large ECE exceeding 6 K in 12CB [24].…”

Synergy of Oxygen Octahedra Distortion and Polar Nanodomains Induced Emergent Electrocaloric Effect in NaNbO3-Based Ceramics

“…As representative lead-free BaTiO 3 ceramic/single crystals, they exhibit first-order transition and present an intense temperature instability around ferroelectric–paraelectric phase transition. − By modifying the BaTiO 3 -based system with an invariant critical point/multiphase coexisting region accompanied by relaxation character, EC performances are improved. However, temperature span still shows a limited expansion. − For example, through merging ferroelectric–ferroelectric and ferroelectric–paraelectric transitions in BaTiO 3 -based ceramics, a broad metastable-phase-transition region is achieved, and EC performance is greatly optimized, which provides a new solution to achieve high EC performance in successive-phase-transition ferroelectrics .…”